Hand-held XRF analyzers are used to detect elements present in a sample. A typical hand-held XRF analyzer includes an x-ray source for directing x-rays to the sample and a detector responsive to the x-rays emitted from the sample. An analyzer processes the output signals produced by the detector and divides the energy levels of the detected x-ray photons into several energy subranges by counts of the number of x-ray photons detected to produce a graph depicting the x-ray spectrum of the sample.
Hand-held XRF analyzers are known. See, e.g., the applicants' co-pending applications, U.S. patent application Ser. No. 11/582,038 filed Oct. 17, 2006 entitled “XRF System with Novel Sample Bottle”, and U.S. patent application Ser. No. 11/585,367 filed Oct. 24, 2006 entitled “Fuel Analysis System”, by one or more common inventors hereof and all of the same assignee, incorporated by reference herein. See also U.S. Pat. Nos. 6,501,825; 6,909,770; 6,477,227; and 6,850,592, all of which are incorporated by reference herein. Using a hand-held XRF analyzer, an operator can detect whether certain elements are present in sample for use in such applications as, inter alia, security and law enforcement, environmental applications, artistic and historic works, biomedical and pharmaceutical applications, process chemistry, and the like. Another key use of hand-held XRF analyzers is to detect elements listed by the European Union Directive Restriction on the Use of Certain Hazardous Substances (RoHs). This Directive restricts the use of certain hazardous substances, such as lead (Pb), mercury (Hg), cadmium (Cd), chromium (Cr) and Bromine (Br), and the like, in manufactured electrical and electronic equipment.
In operation, it is difficult to analyze the low energy x-rays emitted by the electrons of elements having lower atomic numbers, e.g., elements between sodium (Na) and chlorine (Cl). This is because the lower energy of these x-rays is typically reabsorbed by the ambient atmosphere (e.g., air) or the material itself. In order to accurately analyze and detect these lower atomic number elements, the air between the analyzer window and the detector must be removed. This is done either by creating a vacuum or performing a helium (He) purge whereby the helium displaces the air between the analyzer window and the detector. The vacuum or the purge condition prevents the lower energy x-rays from being absorbed into the ambient atmosphere and increases the sensitivity of the XRF analyzer.
However, conventional hand-held XRF analyzers are limited to providing a vacuum or a purge condition, but not both, in a chamber containing the analyzer components. Conventional hand-held XRF analyzers also typically employ a large chamber which increases the time required to create the vacuum or purge condition. The large volume also requires the operator of the analyzer to carry a pump that continuously maintains the desired vacuum or purge condition.
For example, U.S. Pat. No. 6,909,770 to Schramm et al., incorporated by reference herein, relies on a vacuum chamber attachment mounted to the end of a portable XRF analyzer. The sample to be analyzed is placed inside the chamber and the entire volume is evacuated. This approach has the disadvantage of requiring a sample to be removed and placed into the chamber rather than allowing samples to be tested in-situ. The design also requires a larger volume for the vacuum, thus requiring a larger pump which reduces the overall portability of the XRF analyzer.
Other conventional XRF analyzers that utilize a helium purge require an external helium supply. In this design, the operator wears a tank of compressed helium in a backpack with a gas line running into the front snout of the XRF analyzer. The helium gas is continuously flushed through the volume inside the XRF analyzer that includes the air path between the analysis window and the detector. Such designs are cumbersome and difficult to use.
Another conventional XRF analyzer is disclosed in U.S. Pat. No. 7,065,174 to Sipilä, et al., incorporated by reference herein. The XRF analyzer as disclosed by Sipilä, et al. utilizes a removable gas-filled chamber placed inside the volume about the x-ray source, the sample and the detector. The chamber is filled with an appropriate gas, e.g., helium, and hermetically sealed. The chamber is locked into place and used for a period of time. The drop-in chamber is intended to be field replaceable by the end-user. However, the analyzer as disclosed by Sipilä does not offer a way to replenish the purge gas. The chamber must be removed, purged, and replaced. The removal process may compromise expensive and sensitive detector and x-ray tube components situated close by. In practice, most customers do not have the skills to perform this replacement in the field. Thus, a more advantageous design would provide the analyzer with the ability to hold the purge gas for a period of time and alert the operator when the quantity of purge gas was inadequate. Then, the operator could simply connect to a local source of helium gas. However, the analyzer as disclosed by Sipilä et al. fails to teach or disclose these features.
Thus, the conventional hand-held XRF analyzers discussed above are not designed to provide either a vacuum or purge condition as needed and cannot determine if the vacuum or purge condition is being maintained while the analyzer is in operation. Moreover, when the vacuum chamber is integrated with the various components of the analyzer, if the chamber or any of the components fail while the analyzer in operation, the components cannot easily be serviced by the operator in the field. Such a design also prevents the components of the analyzer from being easily upgraded.